The FBI has completed its investigation into the fatal police shooting of Michael Brown, an unarmed, black 18-year-old, in Ferguson, Mo., a U.S. official said Wednesday.

The Justice Department has not yet announced whether it will file a federal civil rights charge against former Ferguson police Officer Darren Wilson. But officials and experts have said such a prosecution would be highly unlikely, in part because of the extraordinarily high legal standard federal prosecutors would need to meet.

The New York Times and CNN, citing unnamed sources, reported Wednesday that Justice Department lawyers were preparing a memo recommending Wilson not be prosecuted; U.S. Atty. Gen. Eric H. Holder Jr. — who is expected to leave his position within weeks — will make the final decision. Ferguson Police Chief Tom Jackson and Mayor James Knowles said Wednesday that they had no information about the status of the investigation.

Benjamin Crump, a lawyer for Brown's family, said in a statement that the family would not address speculation from anonymous officials and was waiting for an official Justice Department announcement.

The U.S. official who spoke to the Associated Press did so on condition of anonymity; the person was not authorized to discuss the case by name. Justice Department spokeswoman Dena Iverson declined to comment.

The Justice Department on Monday issued new guidelines to federal law enforcement officers that will regulate their use of racial profiling in investigations, an update to a policy first put in place in 2003 by then-Atty. Gen. John Ashcroft.

The policy is intended to eliminate discrimination without...

The Justice Department on Monday issued new guidelines to federal law enforcement officers that will regulate their use of racial profiling in investigations, an update to a policy first put in place in 2003 by then-Atty. Gen. John Ashcroft.

The policy is intended to eliminate discrimination without...

(Timothy M. Phelps)

Wilson, who is white, was cleared in November by a state grand jury in the Aug. 9 death of Brown, a shooting that touched off protests in the streets and became part of a national conversation about race relations and police departments that patrol minority neighborhoods. Holder visited Ferguson in the days after the shooting to try to calm tensions and to meet with Brown's relatives and federal law enforcement.

Wilson, who shot Brown after a scuffle in the middle of a street, told the St. Louis County grand jury that he feared for his life during the confrontation and that Brown struck him in the face and reached for his gun. Some witnesses have said Brown had his hands up when Wilson shot him. The grand jury spent months on the case before deciding not to indict Wilson.

The St. Louis suburb of Ferguson, Mo., has been the scene of protests since a white police officer, now identified as six-year veteran Darren Wilson, shot and killed an 18-year old black man on Aug. 9.

To mount a federal prosecution, the Justice Department would need to show that Wilson willfully deprived Brown of his civil rights. That standard, which means prosecutors must prove that an officer knowingly used more force than the law allowed, is challenging to meet. Multiple high-profile police-involved deaths, including the 1999 shooting in New York City of Amadou Diallo, an unarmed West African immigrant, have not resulted in federal charges.

Wilson, who had been on administrative leave since the shooting, resigned days after the grand jury decision was announced. On Wednesday, a lawyer for Wilson did not immediately return a call seeking comment.

A separate, broader Justice Department-led investigation into the practices of the Ferguson Police Department remains open. That investigation, which will examine potential discriminatory practices among officers, has the potential to have more sweeping consequences than any individual criminal prosecution, experts say. The Justice Department has initiated about 20 such investigations of police departments during Holder's tenure.

Meanwhile, the Justice Department is conducting a separate federal civil rights investigation into the death of Eric Garner at the hands of a New York City police officer. In that case too, a local grand jury declined to indict the officer. The U.S. attorney whose office is handling that investigation, Loretta Lynch, has been nominated to replace Holder and faces a Senate confirmation hearing next week.